The present application is related to a co-assigned and co-filed United States patent application entitled In-line Microembossing, Laminating, Printing, and Diecutting. This related application is incorporated herein by reference.
The present invention concerns microembossers, especially those used in the manufacture of holographic labels or stickers.
Holographic labels are used on a variety of articles of manufacture for security, authenticity, or aesthetic appeal. For example, holographic labels are used on credit cards, driver licenses, passports, compact discs, fine jewelry certificates, concert tickets, and magazine covers.
One of the most important steps in manufacturing a holographic sticker or label is known as microembossing. Microembossing is a process of imprinting or cutting microscopic grooves into a layer of material, sometimes called a substrate. For substrates made of a transparent material with a reflective backing, for example, clear plastic with an aluminum coating, the grooves diffract light entering the substrate; the aluminum coating reflects it; and the grooves diffract the reflected light as it exits. If the grooves are arranged in a particular order and cut to appropriate depths, the light entering and exiting the clear plastic diffracts and forms a three-dimensional image, such as the dove commonly found on Visa(trademark) brand credit cards. The microembossed substrate can then be used as part of a holographic label.
Microembossing is usually done using a rotary microembosser. The rotary microembosser typically includes three wide rollers, specifically a shimroller and left and right base rollers. The shimroller, which lies between and contacts the left and right base rollers, includes two steel bars, known as shimclamps, bolted across its width. (Inside the shimroller is a heating element controlled using a temperature sensor that measures surface temperature of the shimroller.) A rectangular stamping shim, bearing twin left and right microgroove patterns on one face, wraps around approximately one-half or two-thirds the circumference of the shimroller, with the shimclamps fastening two opposing edges of the shim against the shimroller and thus preventing either edge from moving during operation of the microembosser.
In operation, the microembosser pulls a long band of reflective plastic, known as a web, left to right through the microembosser, with the web passing first between the left base roller and the shimroller and then between the shimroller and right base roller. As the web passes between the left base roller and the shimroller, the left microgroove pattern on the stamping shim presses into it, transferring the left pattern to a portion of the web. Similarly, as the web passes between the right base roller and shimroller, the stamping shim transfers the right microgroove pattern to an adjacent portion of the web. Thus, as the web feeds through, the embosser embosses a repeating sequence of left and right patterns into the web.
This typical microembosser suffers from at least four problems. First, the two parallel shimclamps, both of which span the width of the shimroller, are cumbersome and time-consuming to install because of the number of bolts, typically 11 per shimclamp, used to secure the shim to the shimroller. Second, the dual, or left-right, base roller, configuration shortens life of the stamping shim and thus forces early shim replacement. Shimlife is shortened because the left and right base roller sequentially move back and forth to press the passing web into the metal stamping shim, flexing the metal shim with every movement.
The third problem concerns the difficulty in timing the back and forth movement of both base rollers so that the left and right patterns cut in the web are accurately and consistently aligned with each other over an entire web length. Misalignment of these two patterns makes it more difficult to align other web processing equipment, such as printers and diecutters, used to manufacture labels with the patterns on the web, ultimately increasing web waste and label-manufacturing costs. Fourth, moving the left and right base rollers back and forth in sequence limits the operating speed of the microembosserxe2x80x94that is, how much web the microembosser can processxe2x80x94to less than 50 linear feet per minute. Ultimately, this limits the production rate of holographic labels.
Accordingly, there is a need for a better microembosser.
To address this and other needs, the inventors have developed a rotary microembosser with a number of unique features. One embodiment of the rotary microembosser includes a single base roller and a shimroller with one or more of the following unique features:
one or more magnetic members that assist in holding a shim;
one or more laterally adjustable shimclamps or shimcollars that facilitate shim installation and adjustment;
an internal temperature sensor that aid control of shimroller temperature;
one or more shimcollars or shimclamps that spans across a gap between the leading and trailing edges of a shim.
One embodiment of the exemplary rotary embosser includes a unique base roller with a Torlon(trademark) polyimide or equivalent sheath for better durability and a lift-off mechanism for automatically separating the base roller from the shimroller during shutdown.